Experimental study of I-caerin 1.1 and I-c(RGD) for internal radiation therapy of esophageal cancer xenografts.

Objective: The aim of this study was to analyze and compare the therapeutic effects of I-caerin 1.1 and I-c(RGD) on TE-1 esophageal cancer cell xenografts.

Methods: (1) The in vitro antitumor effects of the polypeptides caerin 1.1 and c(RGD) were verified by MTT and clonogenic assays. I-caerin 1.1 and I-c(RGD) were prepared by chloramine-T (Ch-T) direct labeling, and their basic properties were measured. The binding and elution of I-caerin 1.1, I-c(RGD), and NaI (control group) in esophageal cancer TE-1 cells were studied through cell binding and elution assays. (2) The antiproliferative effect and cytotoxicity of I-caerin 1.1, I-c(RGD), NaI, caerin 1.1 and c(RGD) on TE-1 cells were detected by Cell Counting Kit-8 (CCK-8) assay. (3) A nude mouse esophageal cancer (TE-1) xenograft model was established to study and compare the efficacy of I-caerin 1.1 and I-c(RGD) in internal radiation therapy for esophageal cancer.

Results: (1) Caerin 1.1 inhibited the in vitro proliferation of TE-1 cells in a concentration-dependent manner, with an IC of 13.00 µg/mL. The polypeptide c(RGD) had no evident inhibitory effect on the in vitro proliferation of TE-1 cells. Therefore, the antiproliferative effects of caerin 1.1 and c(RGD) on esophageal cancer cells were significantly different (P < 0.05). The clonogenic assay showed that the clonal proliferation of TE-1 cells decreased as the concentration of caerin 1.1 increased. Compared with the control group (drug concentration of 0 µg/mL), the caerin 1.1 group showed significantly lower clonal proliferation of TE-1 cells (P < 0.05). (2) The CCK-8 assay showed that I-caerin 1.1 inhibited the in vitro proliferation of TE-1 cells, while I-c(RGD) had no evident inhibitory effect on proliferation. The two polypeptides showed significantly different antiproliferative effects on esophageal cancer cells at higher concentrations (P < 0.05). Cell binding and elution assays showed that I-caerin 1.1 stably bound to TE-1 cells. The cell binding rate of I-caerin 1.1 was 15.8 % ± 1.09 % at 24 h and 6.95 % ± 0.22 % after 24 h of incubation and elution. The cell binding rate of I-c(RGD) was 0.06 % ± 0.02 % at 24 h and 0.3 % ± 0.11 % after 24 h of incubation and elution. (3) In the in vivo experiment, 3 days after the last treatment, the tumor sizes of the phosphate-buffered saline (PBS) group, caerin 1.1 group, c(RGD) group, I group, I-caerin 1.1 group, and I-c(RGD) group were 68.29 ± 2.67 mm, 61.78 ± 3.58 mm, 56.67 ± 5.65 mm, 58.88 ± 1.71 mm, 14.40 ± 1.38 mm, and 60.14 ± 0.47 mm, respectively. Compared with the other treatment groups, the I-caerin 1.1 group had significantly smaller tumor sizes (P < 0.001). After treatment, the tumors were isolated and weighed. The tumor weights in the PBS group, caerin 1.1 group, c(RGD) group, I group, I-caerin 1.1 group, and I-c(RGD) group were 39.50 ± 9.54 mg, 38.25 ± 5.38 mg, 38.35 ± 9.53 mg, 28.25 ± 8.50 mg, 9.50 ± 4.43 mg, and 34.75 ± 8.06 mg, respectively. The tumor weights in the I-caerin 1.1 group were significantly lighter than those in the other groups (P < 0.01).

Conclusion: I-caerin 1.1 has tumor-targeting properties, is capable of targeted binding to TE-1 esophageal cancer cells, can be stably retained in tumor cells, and has an evident cytotoxic killing effect, while I-c(RGD) has no evident cytotoxic effect. I-caerin 1.1 better suppressed tumor cell proliferation and tumor growth than pure caerin 1.1, I-c(RGD), and pure c(RGD).